Harris, from the Rudd Center for Food Policy and Obesity at
Yale University in New Haven, Connecticut, co-wrote an editorial
published with the new study.

"On the one hand schools are trying to teach children about
good nutrition and healthy eating; on the other hand these
companies are actually in the schools promoting their products
directly to children," she told Reuters Health.

In exchange for selling or advertising their products in
schools, corporations will often give school districts a certain
percentage of their sales or donate much-needed supplies.
Companies benefit by increasing brand recognition and brand
loyalty among young customers.

For their study, researchers lead by Yvonne Terry-McElrath
from the University of Michigan in Ann Arbor surveyed a
nationally-representative group of administrators at public
elementary, middle and high schools each year between 2007 and
2012.

They asked administrators about any profits or incentives
their school received from food and beverage companies and if
companies displayed ads or sponsored events.

The study included about 2,400 elementary schools, 800
middle schools and 800 high schools.

The most common form of food commercialism in elementary
schools was awarding coupons as incentives, like for progress in
reading. In 2012, 64 percent of all public elementary school
students went to schools that gave away coupons for food and
drink products.

Older students more often went to schools that had contracts
with beverage companies to exclusively sell their products on
campus. About half of middle school students and 70 percent of
high school students went to schools with those contracts in
2012. Both of those figures had declined somewhat since 2007,
however.

Beverage contracts were especially common at schools with
more disadvantaged and white students, the researchers reported
Monday in JAMA Pediatrics.

Overall, roughly 70 percent of elementary and middle school
students and 90 percent of high school students were exposed to
some type of food commercialism in school.

"I think at the very least, we need to have some good strong
policies that say, hey, you really can't market stuff that's not
healthful for the kids."

She said there has been some progress due to recent
recommendations and voluntary agreements by companies to cut
back on marketing to children.

New nutrition standards from the U.S. Department of
Agriculture will also put more restrictions on what companies
can sell in schools - but they don't address marketing.

Those standards "largely follow the voluntary guidelines
implemented by our industry in 2010," a representative from the
American Beverage Association, a trade group, wrote in a
statement to Reuters Health.

"These guidelines . . . removed full-calorie soft drinks
from schools and replaced them with more lower-calorie,
smaller-portion beverage options. As a result of this
initiative, independent, published studies showed that 90
percent fewer beverage calories were shipped to schools between
2004-2005 and 2009-10."

Parents who are concerned about marketing in schools can
talk with their children, and with administrators, too,
researchers said.

"Ask what the school's policy is," Terry-McElrath advised.
If there's no policy about food and beverage marketing, she
recommended discussing that with the school and looking at
policies in other districts that could be used as a model.

"If parents talk to their kids and ask their kids to look
out for this, this could be a great learning experience," Harris
said.